1. Field of the Invention
The present invention relates to a voice coil motor, and more particularly, to a voice coil motor with a surface coil.
2. Description of the Prior Art
In order to perform a more accurate position control for a set of lenses or an access arm of a hard disk drive, a voice coil motor (VCM) is adopted to move the set of lenses or the access arm of the hard disk drive. The structure of a VCM is primarily a coil placed within a magnetic circuit including a permanent magnet.
In an optical system employing a VCM, a distance at which a set of lenses is moved corresponds to a current flowing through a coil; therefore, when a VCM is utilized to implement the optical zoom functionality, an accurate control can be easily achieved by applying a specific current value. For example, Taiwanese Patent Application No. 1239432 (U.S. Patent Publication No. 2006/0055252), entitled “VOICE COIL MOTOR APPARATUS FOR POSITIONING”, primarily utilizes a magnetic field formed between a coil and a permanent magnet when a current flows through the coil, thereby inducing an interaction propelling force according to Fleming's left-hand rule to move a carrier physically connected to the permanent magnet; at the same time, a set of lenses which is attached to the carrier is moved correspondingly, so as to achieve optical zoom and focus functionalities. In addition to a movable set of lenses, this kind of optical system further requires a more effective positioning technique that does not increase the overall volume.
FIG. 1 is a diagram illustrating a conventional voice coil motor. As shown in FIG. 1, the conventional VCM includes a moving coil 511, fixed next to a lens installation moving pedestal 52 and electronically connected to a VCM pedestal 53 in the fashion of a spiral coil. A magnetic circuit composed of a magnetic stone 513, an upper iron yoke 512 and a lower iron yoke 514 is installed at an inner circular part of an outer casing 50, causing the moving coil 511 to be placed exactly inside an air gap 515 in the magnetic circuit. However, since a space occupied by the copper coil of the moving coil 511 is large, the volume of the conventional VCM is inevitably huge.
In order to achieve a goal of positioning for an optical zoom apparatus which employs a Hall effect, a position feedback sensor, which includes a Hall sensor 45, is fixed onto a printed circuit board (PCB) 542, and the PCB 542 is wedged between the outer casing 50 and the magnetic stone 513. To detect a variation of a magnetic field, the Hall sensor 45 must face the magnetic stone 513, and the Hall sensor 45 outputs a voltage signal via an output terminal 543 as long as the moving coil 511 moves the Hall sensor 45 and the printed circuit board 542 correspondingly. The voltage signal is then processed via a voltage differential amplifier 49, and outputted to a positioning controller 552.
In order to utilize the Hall sensor 45 to act as a sensing element of feedback signals, traces on the PCB 542 must be routed to transmit operation voltages and feedback sensing signals, which not only increases fabrication and assembly costs, but also increases the complexity of an element structural design inside the VCM. The extra space occupied by the Hall sensor 45 also makes the overall volume too large. To subdue the disturbance resulting from the Hall sensor 45, the extra PCB 542 must be utilized more efficiently.